Findings while looking into implementing simultaneous multi-user editing on top of Node.js

I'm pondering developing something to support multiple people editing the same document at the same time.  I thought I'd seen a demo using something like backbone.js,, websockets, or something.  But that was months ago, I can't find it now, and after some searching have come up with some interesting pointers to some stuff but nothing that provides a solid starting point.  Instead I came up with warnings that this is HARD stuff - as in CompSciHard - including one toolkit written by an ex-Google-Wave engineer who said it took them 2 yrs to write Wave, and it would take another 2 yrs